1. Technical Field
The present invention relates to a piezoelectric vibrator element and a piezoelectric module using the same. More particularly, the invention relates to a technique of alleviating the effect on a vibrating portion of stress at a mounting position occurring after mounting.
2. Related Art
In the related art, as a method of mounting piezoelectric vibrator elements, there is known a method of applying a conductive adhesive agent to be bonded to a package. Such a method involves a heat treatment process such as drying for hardening the conductive adhesive agent. Thus, due to a difference in the linear expansion coefficients of the piezoelectric vibrator element, the package, and the conductive adhesive agent, strain remains in the bonded portion of the conductive adhesive agent after cooling. As a result, there is a problem in that stress, namely thermal strain, applied from the bonded portion to a vibrating portion causes an adverse effect on vibration.
Moreover, when the piezoelectric vibrator element is miniaturized, the resonance frequency of the piezoelectric vibrator element may change with time due to the residual stress resulting from the hardened adhesive agent applied to a supporting portion of the piezoelectric vibrator element. Alternatively, it may be necessary to decrease the area of an excitation electrode. As a result, there is a problem in that the electrical properties of the piezoelectric vibrator element deteriorate considerably. For example, the impedance may increase and it may be difficult to obtain favorable properties.
In view of the above problem, JP-A-9-326667 proposes a thickness-shear piezoelectric vibrator such as an AT-cut quartz crystal substrate having a rectangular and flat shape in which a notch or a slit is formed between a supporting portion and a vibrating portion.
FIGS. 21A to 21D show schematic views of a piezoelectric vibrator disclosed in JP-A-9-326667. FIG. 21A is a top view of a piezoelectric vibrator element of the piezoelectric vibrator, FIG. 21B is a bottom view of the piezoelectric vibrator element of the piezoelectric vibrator, FIG. 21C is a plan view of the piezoelectric vibrator in which the piezoelectric vibrator element is mounted inside a container, and FIG. 21D is a cross-sectional view taken along the line A-A′ in FIG. 21C.
FIGS. 21A to 21D show a rectangular piezoelectric vibrator 600 including a supporting portion 602 and a vibrating portion 604. Excitation electrodes 606A and 606B are formed on the upper and lower surfaces of the vibrating portion 604 of the piezoelectric vibrator 600, respectively. Input and output terminal portions 608A and 608B are extracted to the edge of the supporting portion 602 of the piezoelectric vibrator 600 from the excitation electrodes 606A and 606B. A slit 610 is formed on the principal surface of the piezoelectric vibrator 600 between the excitation electrodes 606A and 606B and the input and output terminal portions 608A and 608B. In this way, a structure which physically isolates the excitation electrodes 606A and 606B from the input and output terminal portions 608A and 608B is realized.
In the above configuration, when an adhesive agent 616 for bonding and electrically connecting the supporting portion 602 of the piezoelectric vibrator 600 to a connection electrode (not shown) of a bottom portion 614 inside a container 612 storing the piezoelectric vibrator 600 is hardened, residual stress occurs in the piezoelectric vibrator 600 in the direction and range indicated by the two-dot chain line in FIG. 21C. However, in such a configuration, the slit 610 prevents the residual stress from propagating to the vibrating portion 604. Specifically, by setting the longitudinal length of the slit 610 to an optimal length, the propagation direction of the residual stress can be restricted to the outside of the region indicated by the two-dot chain line. In this way, it is possible to manufacture the compact piezoelectric vibrator 600 with a small change over time in the resonance frequency without deteriorating the electrical properties of the piezoelectric vibrator 600. As similar techniques, a configuration in which a slit is formed between the vibrating portion and a portion where a conductive adhesive agent is applied is disclosed in JP-A-59-040715, JP-UM-61-187116, JP-A-2004-165798, JP-A-2009-158999, and JP-A-2005-136705. Moreover, a configuration in which a notch is formed between the vibrating portion and the conductive adhesive agent applied portion is disclosed in JP-A-59-040715, JP-UM-61-187116, JP-A-2004-165798, JP-A-2009-158999, JP-B-4087186, JP-A-2009-188483, and JP-A-2010-130123. Furthermore, a configuration in which in order to secure rigidity or the like, a depression is formed at the central portion of a piezoelectric vibrator element to realize an inverted mesa structure is disclosed in JP-A-2000-332571, JP-A-2009-164824, and JP-A-2002-246869.
However, in recent years where miniaturization of devices using such a piezoelectric vibrator element and improvement in the performance thereof has advanced rapidly, it has been difficult to sufficiently eliminate the mounting strain with any of the above-described configurations, which is found by the present inventors as described below.
FIGS. 22A and 22B show a stress distribution when a slit is formed between a mount portion and a vibrating portion of a piezoelectric vibrator element. FIG. 22A shows a stress distribution when the width in the Z′-axis direction of the slit of the piezoelectric vibrator element is 150 μm, and FIG. 22B shows a stress distribution when the width in the Z′-axis direction of the slit of the piezoelectric vibrator element is 250 μm. Moreover, FIGS. 23A to 24B show stress distributions when a notch is formed on both sides in the width direction of the piezoelectric vibrator element at a position between the mount portion and the vibrating portion to thereby form a connecting portion that connects the mount portion and the vibrating portion together. FIG. 23A shows a stress distribution when the width in the X-axis direction of the connecting portion is 400 μm, and FIG. 23B shows a stress distribution when the width in the X-axis direction of the connecting portion is 300 μm. Moreover, FIG. 24A shows a stress distribution when the width in the X-axis direction of the connecting portion is 200 μm, and FIG. 24B shows a stress distribution when the width in the X-axis direction of the connecting portion is 100 μm.
FIGS. 22A to 24B show simulation results of a stress distribution when compressive stress or tensile stress is applied to a piezoelectric vibrator element 700 at two positions corresponding to the centers of two circles on the surface on the Y′-axis side of a mount portion 702 to which a conductive adhesive agent is applied in the drawings. The compressive stress or tensile stress (residual stress) occurs due to stress applied to the piezoelectric vibrator element resulting from a difference in the thermal expansion coefficients of the piezoelectric vibrator element, the conductive adhesive agent, and the substrate.
In FIGS. 22A to 24B, the X, Y′, and Z′ axes are assumed to be orthogonal to each other, and the piezoelectric vibrator element 700 has a planar outer shape which has principal surfaces normal to a direction parallel to the Y′ axis and side edges in a direction parallel to the Z′ axis and a direction parallel to the X axis. Moreover, a slit 704 is formed as a penetration hole penetrating through the principal surfaces of the piezoelectric vibrator element 700. Thus, in the piezoelectric vibrator element 700, the mount portion 702, the slit 704, and the vibrating portion 706 are arranged in a laterally parallel form. In FIGS. 22A and 22B, the piezoelectric vibrator element 700 has such an outer shape that the length in the arrangement direction (the Z′-axis direction) in which the mount portion 702, the slit 704, and the vibrating portion 706 are arranged is 1500 μm, and the width in the X-axis direction is 1000 μm. Moreover, the length in the X-axis direction (long side) of the slit 704 is 650 μm. In addition, the width in the Z′-axis direction from the long side of the slit 704 on the mount portion 702 side to the end portion of the mount portion 702 is 350 μm in FIG. 22A and is 250 μm in FIG. 22B. Moreover, the width in the Z′-axis direction of the slit 704 is 150 μm in FIG. 22A and is 250 μm in FIG. 22B. That is, the position and width in the Z′-axis direction of the slit 704 is changed between FIG. 22A and FIG. 22B.
Moreover, a plurality of patterns arranged in a vertical line to the left of the drawings of FIGS. 22A to 24B represents the intensity of stress applied to the piezoelectric vibrator element 700. The higher the pattern, the greater the stress, and the lower the pattern, the smaller the stress. Moreover, the distribution of the intensity of stress applied to the piezoelectric vibrator element 700 is depicted using the patterns described above.
As shown in FIGS. 22A and 22B, in such a compact piezoelectric vibrator element 700, it can be understood that even when the slit 704 is disposed, and moreover, the position and width of the slit 704 are changed, it is very difficult to eliminate stress resulting from the stress occurring in the mount portion 702, but strong stress reaches up to the vibrating portion 706 of the piezoelectric vibrator element 700. Thus, there is a problem in that the stress has an adverse effect on the electrical properties such as stability of the resonance frequency of the piezoelectric vibrator element 700.
A piezoelectric vibrator element 700 shown in FIGS. 23A to 24B has a so-called notch structure in which notches 708 are formed at both ends in the width direction of the piezoelectric vibrator element 700 at a position between the mount portion 702 and the vibrating portion 706 according to the related art disclosed in JP-A-2005-136705 and JP-B-4087186. In this structure, it can be understood that when the width of a connecting portion 710 formed by the notches 708 is decreased, the propagation of stress occurring in the mount portion 702 to the vibrating portion 706 is alleviated. However, a structure in which the vibrating portion 706 is supported by only the connecting portion 710 has drawbacks in terms of its strength such as drop impact resistance and lacks practical application.